Amphioxi populated the oceans about 550 million years ago

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A note for The Half-Lesson, "Your Brain Is Not for Thinking," in Seven and a Half Lessons About the Brain by Lisa Feldman Barrett.
Some context from page 1 is:

Amphioxi populated the oceans about 550 million years ago, and they lived simple lives.

The appendix adds:

Amphioxi are our evolutionary cousins.... [They] lack all sorts of features that distinguish vertebrates from invertebrates.

For technical information on the amphioxus and its evolution, as well as references to other useful papers, please see these books and papers.[1][2][3][4][5][6][7][8]

To learn how vertebrates developed eyes and ears and so on, see Neil Shubin’s informative and easy-to-read telling of the evolutionary story.[9]


  1. Bertrand, Stephanie and Hector Escriva. 2011. “Evolutionary Crossroads in Developmental Biology: Amphioxus.” Development 138 (22): 4819–4830.
  2. Cisek, Paul. 2019. "Resynthesizing behavior through phylogenetic refinement." Attention, Perception and Psychophysics 81 (7): 2265–2287.
  3. Gee, Henry. 2018. Across the Bridge: Understanding the Origin of the Vertebrates. Chicago, IL: University of Chicago Press.
  4. Lacalli, Thurston C. 2004. “Sensory Systems in Amphioxus: A Window on the Ancestral Chordate Condition.” Brain, Behavior and Evolution 64 (3): 148–162.
  5. Lacalli, Thurston C. 2008. “Basic Features of the Ancestral Chordate Brain: A Protochordate Perspective.” Brain Research Bulletin 75 (2-4): 319–323.
  6. Lacalli, Thurston C. 2018. "Amphioxus neurocircuits, enhanced arousal, and the origin of vertebrate consciousness." Consciousness and Cognition 62:127–134.
  7. Striedter, Georg F., and R. Glenn Northcutt. 2020. Brains Through Time: A Natural History of Vertebrates. New York: Oxford University Press.
  8. Wicht, Helmut and Thurston C. Lacalli. 2005. “The Nervous System of Amphioxus: Structure, Development, and Evolutionary Significance.” Canadian Journal of Zoology 83 (1): 122–150.
  9. Shubin, Neil. 2008. Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body. New York: Pantheon.